In clinical application, the computed tomography scanner is used to acquire a data record for an X-ray image, on the basis of which a specific material is determined within an object to be examined or a patient. The aspect of material determination is becoming ever more important in routine clinical problems and so the importance and field of application of computed tomography scanners has greatly increased.
A computed tomography scanner used to recognize material during the evaluation and display of X-ray data operates on the principle of the so-called dual-energy method. In this method, the object to be examined or the patient is for example scanned with X-ray quanta up to 80 keV and X-ray quanta up to 140 keV. Here, it is possible to either use two X-ray emitters with different energies or switch the tube voltage of an X-ray emitter alternately. As a result of the different X-ray spectra of the two X-ray radiations, a differing average attenuation is generated and so more comprehensive information is gathered compared to a conventional computed tomography scanner in normal operation.
DE 10 2004 031 168 A1 describes an imaging X-ray scanner in which a two-part filter is inserted into a fan-beam-shaped beam path. The two parts of the filter arranged next to each other in the radiation direction divide the fan beam into two beam fans which differ in respect of the intensity thereof.
U.S. Pat Nos. 7,463,715 and 7,116,749 systems for dual-energy visualization, in which a rotating X-ray filter is positioned in the X-ray beam and so the spectrum of the X-ray radiation changes as a result of the rotation of the X-ray filter. Here, images are recorded alternately for each position, with each image corresponding to a different X-ray spectrum.